Hi Hans,
As a teenager, I worked as a metal plater and etcher for two
printed circuit shops. At some point during my employ, they
tasked me with every operation in PCB manufacture.
The PCB shops that I worked for, generally drilled their holes
with the closest sized drills in their tool crib, equal to, or
larger than the drill sizes listed in the customer's tool list.
In addition, the first hole drilled by a given drill is measurably
larger than the last hole drilled by that drill... wear happens.
Manufacturers are motivated to use a drill for just as long as it
will drill effectively, and the hole diameter meets the customer's
tolerance band... some will use them for quite a bit longer...
Where some major contention invariably happens is plated-through
holes.
When a hole is plated, the as-drilled size is reduced by the
thickness of the hole's plating, which is typically 0.1-0.2mm,
to create the finished hole size.
Most manufacturers expect you to give them the as-drilled size
in your tool list, but others expect to be given the finished
hole size.
Manufacturers will generally reveal the necessary hole size
information somewhere in their contract's boiler plate. Customers
will generally ignore that boiler plate, imagining that things
will work out OK by default.
I know that you may already know all of this, but I choose to
mention it anyway for two reasons: 1) general knowledge, and
2) because many of the holes in my QMX+ PCB seem about a plating
allowance too tight... while others (connectors, switches) are
grossly big, and yet still ill-fitting. I can only guess at the
whys and wherefores....
-Chuck Harris, WA3UQV
On Fri, 23 May 2025 11:56:32 +0300 "Hans Summers via groups.io"
<hans.summers@...> wrote:
Hi Tony
I just measured one of the 1N4007 diodes from the kits, the wire
diameter is 0.4mm. According to the PCB CAD program (I just checked)
the footprint for these diodes specifies a 0.8mm drill size. So the
holes ought to fit 0.7mm wire too.
73 Hans G0UPL
